A topsheet used in absorbent articles, such as sanitary napkins and disposable diapers, is required to have not only absorbing performance for smoothly passing liquid body waste, e.g., menstrual blood or urine, to an underlying absorbent member but surface characteristics for causing neither discomfort due to overhydration nor skin troubles such as an itch and a rash.
To meet these requirements various topsheets with an uneven surface on the wearer's side have been proposed for application to absorbent articles.
JP-A-9-111631 discloses wrinkled nonwoven fabric with a great number of streaky wrinkles (ridges) arrayed on its surface, which is used as a topsheet of an absorbent article such as a disposable diaper or a sanitary napkin. The wrinkled nonwoven fabric is produced by superposing a heat non-shrinkable fiber layer on a layer comprising heat shrinkable fiber and heat bondable fiber whose melting point is lower than the shrinkage starting temperature of the heat shrinkable fiber, joining the two layers by applying heat in stripes, and shrinking the fiber layer containing the shrinkable fiber to deform the other fiber layer. Because the shrunken fiber layer has an increased thickness, the whole sheet lacks sufficient softness. Further, the structure is not such that allows the liquid discharged on the surface to quickly migrate into the underlying absorbent member. As a result, the liquid tends to remain on the surface to cause overhydration or skin troubles. When this sheet is used as a topsheet of a sanitary napkin, the color of remaining blood is noticeable, giving a dirty impression to a user.
JP-A-7-232409 discloses composite nonwoven fabric composed of a textured synthetic resin film with a grain pattern and an extensible nonwoven fabric. Having a grain pattern, the composite fabric is soft and matte. However, the fabric easily bunches up, and the resin film side easily makes large wrinkles when bent. Therefore, an absorbent article having the composite fabric as a topsheet comes to have poor fit to a wearer's body, and liquid is apt to flow along the wrinkles to cause a leak. Where, in particular, used as a topsheet of a sanitary napkin, which is usually packaged as folded into three, wrinkles occur easily to invite leakage.
JP-A-9-3755 discloses nonwoven fabric with a textured surface designed to serve as a female member of a mechanical fastener in disposable diapers, etc., which is produced by superposing a layer containing heat shrinkable fiber and a layer containing heat non-shrinkable fiber, and heat embossing the two layers thereby bonding the two layers in parts and simultaneously causing the layer containing the heat shrinkable fiber to shrink.
In nonwoven fabrics of the type which are produced by joining a layer comprising heat shrinkable fiber and a layer comprising non-shrinkable fiber and shrinking the layer comprising heat shrinkable fiber, such as those proposed in JP-A-9-111631 and JP-A-8-3755 described supra, a web or nonwoven fabric is used as the layer comprising heat shrinkable fiber. A web needs care in handling because it tears easily due to low strength and also fuzzes easily. Nonwoven fabric, on the other hand, should be produced without involving heat application. Nonwoven fabrics fabricated with no heat application include needle punch nonwoven, spunlace nonwoven, and resin bond nonwoven. Such nonwoven products are costly because of low production speeds, as seen from the fact that their application has been limited to relatively expensive cataplasms. Besides, it is difficult to produce nonwoven products of small basis weight by these nonwoven techniques.
JP-A-1-201569 proposes bulky reinforced nonwoven fabric composed of a fiber web and monofilaments fixed to the web, the monofilaments having shrunken to wrinkle the web. The monofilaments are not a fiber layer having high densified parts which is used in the present invention. JP-A-2-221450 teaches a process of making highly extensible nonwoven fabric comprising heat treating a web of self-crimping conjugate fiber. According to the process, the heat treatment is carried out simultaneously with embossing so that the resulting nonwoven fabric is a shrunken product.